XI
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TABLE OF CONTENTS
ABSTRACT... I RÉSUMÉ ... V ACKNOWLEDGEMENT ... VII TABLE OF CONTENTS ... XI LIST OF ABBREVIATIONS ... XV I. CHAPTER I: Introduction ... 1 I.1. Motivation ... 1I.2. Thesis outlines ... 3
II. CHAPTER II: State of the art ... 5
II.1. The climatic relevance of CO2 and N2O in the polar marine environment ... 5
II.1.1. A quick look at the global warming main cause and feedback on sea ice melt ... 5
II.1.2. A positive feedback on sea ice melt: the decreasing albedo ... 5
II.1.3. Atmospheric relevance of CO2 and N2O ... 6
II.1.4. The marine cycle of carbon and nitrogen ... 8
II.2. From a free-ice to an ice-covered seawater ... 10
II.2.1. Sea ice formation conditions and its resulting structure ... 10
II.2.2. Sea ice growth ... 12
II.2.3. Sea ice texture ... 12
II.3. The significant role of salts in sea ice ... 16
II.3.1. What does salinity profiles state ... 16
II.3.2. Brine volume fraction and brine salinity relationships ... 17
II.3.3. Brine concentration and dilution ... 19
II.3.4. Permeability threshold for liquid brine ... 19
II.3.5. Desalinisation processes ... 20
II.4. Gas bubbles within sea ice ... 23
II.4.1. Gas bubbles formation ... 23
II.4.2. Total gas content ... 24
II.4.3. Permeability thresholds for gas bubbles ... 24
XII
II.5.2. Gas diffusion ... 27
II.6. CO2 dynamics within the ice and at the interfaces ... 28
II.6.1. Overview of the carbonate chemistry system ... 28
II.6.2. The carbonate system within sea ice ... 29
II.6.3. CO2 exchanges at the sea ice–seawater interface ... 31
II.6.4. CO2 fluxes at the atmosphere–sea ice interface ... 31
II.7. N2O dynamics within the ice and the seawater ... 33
II.7.1. Processes controlling N2O concentration ... 33
II.7.2. The N2O dynamic in the Arctic Ocean ... 35
II.7.3. The N2O dynamic in sea ice ... 37
II.8. The Arctic Ocean ... 39
II.8.1. Arctic Ocean topography ... 39
II.8.2. Arctic Ocean circulation ... 40
III. CHAPTER III: The impact of dissolved organic carbon and bacterial respiration on pCO2 in experimental sea ice ... 43
Abstract ... 44
III.1. Introduction ... 44
III.2. Material and methods... 45
III.2.1. Experimental setting, and sampling routine and initial conditions .. ... 45
III.2.2. Brine volume fraction and Raleigh number ... 46
III.2.3. DOC and DON ... 46
III.2.4. Bacterial respiration ... 46
III.2.5. pCO2 ... 46
III.2.6. TA and DIC ... 47
III.2.7. Differences between the SW and SWR series and statistical tests 47 III.3. Results ... 47
III.3.1. Physical sea ice conditions ... 47
III.3.2. DOC and DON ... 47
III.3.3. Bacterial activity ... 48
III.3.4. DIC7 ... 49
III.3.5. pCO2 ... 49
III.4. Discussion ... 49
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III.4.2. Similarities of DIC and pCO2 in ice in the SW and SWR mesocosms
... 51
III.4.3. Differences of DIC and pCO2 in ice between the SW and SWR mesocosms ... 52
III.4.4. Modelling the impact of bacterial respiration on pCO2 in ice ... 53
III.5. Conclusion and large scale implications ... 56
IV. CHAPTER IV: Air–ice carbon pathways inferred from a sea ice tank experiment ... 57
Abstract ... 58
IV.1. Introduction ... 58
IV.2. Methods ... 59
IV.2.1. Experimental setting ... 59
IV.2.2. Ice pCO2 at high vertical resolution ... 59
IV.2.3. Total alkalinity ... 60
IV.2.4. Dissolved inorganic carbon ... 60
IV.2.5. Seawater pCO2 ... 60
IV.2.6. Air–ice CO2 fluxes ... 60
IV.2.7. Assessment of the precision of derived variables ... 61
IV.2.8. Modelling air–ice CO2 fluxes ... 61
IV.3. Results and discussion... 62
IV.3.1. Total alkalinity ... 63
IV.3.2. CO2 exchange at the air–ice interface ... 63
IV.3.3. Determination of a gas transfer coefficient for CO2 in artificial sea ice ... 65
IV.3.4. Model sensitivity experiments on the CO2 transport pathways through sea ice ... 66
IV.3.5. Synthesis ... 67
IV.4. Conclusions ... 69
V. CHAPTER V: Winter to spring ocean̶̶̶̶ sea ice̶ atmosphere N2O partitioning in the Arctic Ocean (north of Svalbard) ... 71
Abstract ... 72
V.1. Introduction ... 72
V.2. Sampling area ... 75
V.3. Material and methods... 77
V.3.1. Seawater sampling (on-ice and ship rosette) ... 77
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V.3.3. Snow sampling ... 79
V.3.4. Nutrients and dissolved oxygen analysis ... 79
V.3.5. Oxygen isotope analysis ... 80
V.3.6. N2O concentration analysis ... 80
V.3.7. Chl a analysis ... 81
V.3.8. Calculation for N* and AOU ... 82
V.3.9. Calculation for brine volume and brine salinity ... 82
V.3.10. Cross-variable statistics ... 82
V.4. Results ... 83
V.4.1. N2O distribution within the water masses ... 83
V.4.2. Temporal and spatial variation of N2O in the water column ... 84
V.4.3. Biological properties of the water column ... 85
V.4.4. Relationships to freshwater fractions, sea ice meltwater fraction and brine rejection ... 85
V.4.5. Sea ice biogeochemistry... 87
V.5. Discussion ... 90
V.5.1. Origin of N2O undersaturation in surface waters ... 90
V.5.2. Origin of the N2O enrichment in PSW ... 94
V.5.3. N2O concentration in first and second-year sea ice ... 96
V.5.4. N2O exchanges at the air–ice interfaces ... 98
V.5.5. Biological and chemical production of N2O taking place at the snow– ice interface ... 99
V.6. Conclusion ... 101
Acknowledgements ... 102
VI. CHAPTER VI: Conclusions ... 103
VI.1. Synthesis of the INTERICE V findings on the CO2 content ... 103
VI.2. Determination of an air-ice gas transfer coefficient for CO2 ... 105
VI.3. N2O distribution in the Arctic Ocean ... 106
VI.4. Perspectives: Arctic sea ice CO2 and N2O dynamics in a changing environment ... 109
REFERENCES ... 113
APPENDIX A: List of publications ... 133
